Method of producing unsaturated acid in fixed-bed catalytic partial oxidation reactor with high efficiency

ABSTRACT

A shell-and-tube heat exchanger-type reactor including one or more catalytic tubes, each including a first-step reaction zone and a second-step reaction zone, wherein at least one of the first-step reaction zone and the second-step reaction zone is divided into two or more shell spaces by a partition; each of the divided shell spaces is independently heat-controlled; and a heat transfer medium having a temperature from the lowest active temperature of a catalyst layer in a reaction tube corresponding to the first shell space of the first-step reaction zone or the first shell space of the second-step reaction zone to the lowest active temperature of the catalyst layer plus 20° C.; and the first shell space of the first-step reaction zone or the first shell space of the second-step reaction zone is controlled so as to provide a reactant conversion contribution per length of 1.2˜2.5.

This application is a divisional of U.S. application Ser. No.11/483,752, filed Jul. 10, 2006, which claims the benefit of the filingdate of Korean Patent Application No. 2005-61797, filed on Jul. 8, 2005,in the Korean Intellectual Property Office. The disclosure of bothapplications is incorporated herein in their entirety by reference.

TECHNICAL FIELD

The present invention relates to a process for producing unsaturatedaldehydes and/or unsaturated acids from olefins or alkanes in a fixedbed shell-and-tube heat exchanger-type reactor by catalytic vapor phaseoxidation, as well as a heat exchanger-type reactor for use in the sameprocess.

BACKGROUND ART

A process for producing unsaturated aldehydes and/or unsaturated acidsfrom olefins or alkanes in vapor phase by using a catalyst is a typicalprocess of catalytic vapor phase oxidation.

Particular examples of such catalytic vapor phase oxidation include aprocess for producing acrolein and/or acrylic acid by the oxidation ofpropylene or propane, or a process for producing methacrolein and/ormethacrylic acid by the oxidation of isobutylene, isobutane, t-butylalcohol or methyl t-butyl ether.

Generally, catalytic vapor phase oxidation is carried out by chargingone or more kinds of granular catalysts into a reaction tube (catalytictube), supplying feed gas into a reactor through a pipe, and contactingthe feed gas with the catalyst in the reaction tube. Reaction heatgenerated during the reaction is removed by heat exchange with a heattransfer medium whose temperature is maintained at a predeterminedtemperature. The heat transfer medium for heat exchange is provided onthe outer surface of the reaction tube so as to perform heat transfer.The reaction mixture containing a desired product is collected andrecovered through a pipe, and sent to a purification step. Since thecatalytic vapor phase oxidation is a highly exothermic reaction, it isvery important to maintain reaction temperature within a certain rangeand to reduce the magnitude of a hot spot occurring in a reaction zone.It is also very important to disperse heat at a site where heataccumulation may occur due to the structure of a reactor or a catalystlayer.

The partial oxidation of olefins or alkanes corresponding thereto uses amultimetal oxide containing molybdenum and bismuth or vanadium or amixture thereof, as a catalyst.

Generally, (meth)acrylic acid, a final product, is produced frompropylene, propane, isobutylene, isobutane, t-butyl alcohol ormethyl-t-butyl ether (referred to as ‘propylene or the like’,hereinafter) by a two-step process of vapor phase catalytic partialoxidation. More particularly, in the first step, propylene or the likeis oxidized by oxygen, inert gas for dilution, water steam and a certainamount of a catalyst, so as to produce (meth)acrolein as a main product.Then, in the second step, the (meth)acrolein is oxidized by oxygen,inert gas for dilution, water steam and a certain amount of a catalyst,so as to produce (meth)acrylic acid. The catalyst used in the first stepis a Mo—Bi-based oxidation catalyst, which oxidizes propylene or thelike to produce (meth)acrolein as a main product. Also, some acrolein iscontinuously oxidized on the same catalyst to partially produce(meth)acrylic acid. The catalyst used in the second step is a Mo—V-basedoxidation catalyst, which mainly oxidizes (meth)acrolein in the mixedgas containing the (meth)acrolein produced from the first step toproduce (meth)acrylic acid as a main product.

A reactor for performing the aforementioned process is provided eitherin such a manner that both the two-steps can be performed in one system,or in such a manner that the two steps can be performed in differentsystems.

Recently, a catalyst for use in producing unsaturated acids such as(meth)acrylic acid from alkanes such as propane or isobutane via asingle-step process has been developed.

Meanwhile, (meth)acrylic acid manufacturers now conduct diversifiedefforts either to improve the structure of the reactor so as to increasethe production of acrylic acid by the reactor, or to propose the mostsuitable catalyst to induce oxidation, or to improve process operations.

In part of such prior efforts, propylene or the like which is suppliedinto the reactor is used at high space velocity and high concentration.However, in this case, rapid oxidation occurs in the reactor, whichmakes it difficult to control the resultant reaction temperature. Also,a hot spot is generated in the catalyst layer of the reactor, and heataccumulation occurs in the vicinity of the hot spot, resulting inincreased production of byproducts, such as carbon monoxide, carbondioxide and acetic acid at high temperature, and in a drop in yield of(meth)acrylic acid.

Furthermore, production of (meth)acrylic acid using high space velocityand high concentration of propylene or the like causes various problems,as the reaction temperature abnormally increases in the reactor, suchproblems including the loss of active ingredients from the catalystlayer, a drop in the number of active sites caused by sintering of metalcomponents, or the like. Consequently, this leads to deterioration ofthe function of the catalyst layer.

Accordingly, in the production of (meth)acrylic acid, control of thereaction heat in the relevant reactor is of great importance.Particularly, not only the formation of hot spots in the catalyst layerbut also the accumulation of heat in the vicinity of the hot spots mustbe inhibited, and the reactor must be effectively controlled so that thehot spots do not lead to reactor runaway (a state where the reactorcannot be controlled or explodes by a highly exothermic reaction).Therefore, it is very important to inhibit hot spots and heataccumulation in the vicinity of the hot spots so as to extend thelifetime of the catalyst, to inhibit side reactions, and thus toincrease yield of (meth)acrylic acid.

DISCLOSURE OF THE INVENTION

The inventors of the present invention have made improvements in afixed-bed shell-and-tube heat exchanger-type reactor for producingunsaturated aldehydes and/or unsaturated acids from olefins. In theimprovements, at least one reaction zone of the first-step reaction zoneand the second-step reaction zone was divided into two or more shellspaces along the axial direction by at least one partition, and thetemperature of a heat transfer medium filled in each of the dividedshell spaces was set to a temperature suitable for the activity of acatalyst and the degree of reaction. As a result of such improvements,the present inventors have found that a hot spot and heat accumulationin the vicinity of the hot spot could be inhibited. The presentinvention is based on this finding.

Additionally, the present invention may be applied to a single-stepprocess for producing unsaturated acids from alkanes, for example, aprocess for producing (meth)acrylic acid from propane or isobutane.

In one aspect, the present invention provides a process for producingunsaturated aldehydes from olefins, particularly a process for producing(meth)acrolein from propylene or the like, by fixed-bed catalyticpartial oxidation in a shell-and-tube heat exchanger-type reactor,wherein the reactor comprises a reaction zone for producing theunsaturated aldehydes; the reaction zone is divided into two or moreshell spaces by at least one partition; each of the divided shell spacesis independently heat-controlled; a heat transfer medium in the firstshell space has a temperature ranging from the lowest active temperatureof a catalyst layer packed in a reaction tube corresponding to the firstshell space to [the lowest active temperature+20° C.], when referring tothe two or more shell spaces sequentially as the first shell space, thesecond shell space, . . . , the n^(th) shell space; and the first shellspace is controlled in such a manner that it provides an olefinconversion contribution per length as defined in the following equationof 1.2˜2.5:

Olefin conversion contribution per length=(mole number of olefins thathave reacted in the relevant catalyst layer zone/mole number of thetotal olefins supplied to the reaction zone)/volumetric ratio of therelevant catalyst layer zone to the total catalyst layer of the reactionzone.  [Equation 1]

In another aspect, the present invention provides a process forproducing unsaturated acids from unsaturated aldehydes or alkanes,particularly a process for producing (meth)acrylic acid from(meth)acrolein, propane or isobutane, by fixed-bed catalytic partialoxidation in a shell-and-tube heat exchanger-type reactor, wherein thereactor comprises a reaction zone for producing the unsaturated acids;the reaction zone is divided into two or more shell spaces by at leastone partition; each of the divided shell spaces is independentlyheat-controlled; a heat transfer medium in the first shell space has atemperature ranging from the lowest active temperature of a catalystlayer packed in a reaction tube corresponding to the first shell spaceto [the lowest active temperature+20° C.], when referring to the two ormore shell spaces sequentially as the first shell space, the secondshell space, . . . , the n^(th) shell space; and the first shell spaceis controlled in such a manner that it provides an unsaturated aldehydeor alkane conversion contribution per length as defined in the followingequation of 1.2˜2.5:

Unsaturated aldehyde or alkane conversion contribution per length=(molenumber of unsaturated aldehydes or alkanes that have reacted in therelevant catalyst layer zone/mole number of the total unsaturatedaldehydes or alkanes supplied to the reaction zone)/volumetric ratio ofthe relevant catalyst layer zone to the total catalyst layer of thereaction zone.  [Equation 2]

In still another aspect, the present invention provides a shell-and-tubeheat exchanger-type reactor which can be used in a process for producingunsaturated aldehydes and unsaturated acids from olefins by fixed-bedcatalytic partial oxidation, the reactor comprising one or morecatalytic tubes each including a first-step reaction zone for mainlyproducing the unsaturated aldehydes, and a second-step reaction zone formainly producing the unsaturated acids, or both the two zones, whereinat least one of the first-step reaction zone and the second-stepreaction zone is divided into two or more shell spaces by at least onepartition; each of the divided shell spaces is independentlyheat-controlled; a heat transfer medium in the first shell space of thefirst-step reaction zone or the first shell space of the second-stepreaction zone has a temperature ranging from the lowest activetemperature of a catalyst layer packed in a reaction tube correspondingto the first shell space of the first-step reaction zone or the firstshell space of the second-step reaction zone to [the lowest activetemperature+20° C.], when referring to the two or more shell spacescorresponding to the first-step reaction zone sequentially as the firstshell space of the first-step reaction zone, the second shell space ofthe first-step reaction zone, . . . , the n^(th) shell space of thefirst-step reaction zone, and the two or more shell spaces correspondingto the second-step reaction zone sequentially as the first shell spaceof the second-step reaction zone, the second shell space of thesecond-step reaction zone, . . . , the n^(th) shell space of thesecond-step reaction zone; and the first shell space of the first-stepreaction zone or the first shell space of the second-step reaction zoneis controlled in such a manner that it provides a reactant conversioncontribution per length as defined in Equation 1 or 2 of 1.2˜2.5.

In yet another aspect, the present invention provides a shell-and-tubeheat exchanger-type reactor which can be used in a process for producingunsaturated acids from alkanes by fixed-bed catalytic partial oxidation,the reactor comprising one or more catalytic tubes each including areaction zone for producing the unsaturated acids, wherein the reactionzone is divided into two or more shell spaces by at least one partition;each of the divided shell spaces is independently heat-controlled; aheat transfer medium in the first shell space has a temperature rangingfrom the lowest active temperature of a catalyst layer packed in areaction tube corresponding to the first shell space to [the lowestactive temperature+20° C.], when referring to the two or more shellspaces sequentially as the first shell space, the second shell space, .. . , the n^(th) shell space; and the first shell space is controlled insuch a manner that it provides an alkane conversion contribution perlength as defined in Equation 2 of 1.2˜2.5.

Hereinafter, the present invention will be explained in more detail.

(1) Disposition of Partition

The inventors of the present invention have conducted many studies andobtained the following results. When a catalyst having a high activitycorresponding to a conversion of 96% or more in the first-step-reactionzone (for example, a catalyst having a conversion of 96% at atemperature, where the highest catalytic activity can be obtained, undera space velocity of feed of 1500 hr⁻¹ and that of an olefin of 100 hr⁻¹)is packed in the first-step reaction zone and the reaction zone isoperated with no temperature control along the axial direction, a hotspot having a temperature near the sintering temperature of the catalystis generated in the front portion of the first-step reaction zone.Additionally, when a catalyst having a high activity corresponding to anacrolein conversion of 95% or more in the second-step reaction zone (forexample, a catalyst having a conversion of 95% at a temperature, wherethe highest catalytic activity can be obtained, under a space velocityof unsaturated aldehydes of 90 hr⁻¹) is packed in the second-stepreaction zone and the reaction zone is operated with no independenttemperature control along the axial direction, a hot spot having atemperature near the sintering temperature of the catalyst is generatedin the front portion of the second-step reaction zone. Such problem ofhot spots also occurs in a single-step process for producing unsaturatedacids from alkanes.

In addition, it is not possible to sufficiently control the reactionheat of catalytic vapor phase oxidation mere by circulating a heattransfer medium uniformly in a reactor. A large hot spot is generatedfrequently, thereby causing excessive oxidation in a local site in thereactor. As a result, undesirable oxidation increases, resulting in adrop in yield of the target product. Moreover, catalysts are locallyexposed to high temperature conditions caused by the presence of a hotspot, resulting in degradation in lifetime of the catalysts.

A hot spot refers to a site where the highest temperature peak isgenerated, and is formed by the generation of reaction heat caused bycatalytic vapor phase oxidation. The hot spot is determined by thecomposition of reactants, the flow rate (L/min) of the reactants, thetemperature of a heat transfer medium, etc., and has a certain positionand magnitude under a certain process condition. Generally, eachcatalytic layer has at least one hot spot. However, since the activityof a catalyst varies with time, the position and temperature of a hotspot may also be varied.

According to the present invention, a partition is disposed in such amanner that each shell space divided by the partition has at least onetemperature peak, after the characterization of the temperature profileof a catalyst layer. By doing so, a hot spot and zones near the hot spothaving the possibility of heat accumulation can be heat-controlledintensively in an independent heat-control space. As used herein, theterm “each divided shell space” indicates an internal space surroundedby a catalytic tube, a shell, a partition, a tube sheet, etc.

In each reaction zone, the portions where heat control is problematicdue to the hot spot include the front portion of a catalyst layer, inwhich main reactants including olefins, alkanes or unsaturatedaldehydes, and molecular oxygen, are present at high concentrations.Also, if two or more catalyst layers are used in each step, suchproblematic portions include the vicinity of the boundary between theadjacent catalyst layers having different activities.

The partition is preferably located at either a position where heatcontrol is problematic due to the hot spot or heat accumulation causedby the hot spot, or a position allowing the largest possible removal ofheat generation in each zone.

Additionally, when each reaction zone is divided into two or more shellspaces by using at least one partition and is subjected to heat control,it is possible to provide the process with high flexibility under thevariations in temperature profile characteristics.

(2) Heat Control of Heat Transfer Medium of the First Shell Space ofEach Step

According to an aspect of the present invention, at least one of thefirst-step reaction zone and the second-step reaction zone is dividedinto two or more shell spaces by at least one partition; each of thedivided shell spaces is independently heat-controlled; a heat transfermedium in the first shell space of the first-step reaction zone or thefirst shell space of the second-step reaction zone has a temperatureranging from the lowest active temperature of a catalyst layer packed ina reaction tube corresponding to the first shell space of the first-stepreaction zone or the first shell space of the second-step reaction zoneto [the lowest active temperature+20° C.], when referring to the two ormore shell spaces corresponding to the first-step reaction zonesequentially as the first shell space of the first-step reaction zone,the second shell space of the first-step reaction zone, . . . , then^(th) shell space of the first-step reaction zone, and the two or moreshell spaces corresponding to the second-step reaction zone sequentiallyas the first shell space of the second-step reaction zone, the secondshell space of the second-step reaction zone, . . . , the n^(th) shellspace of the second-step reaction zone (wherein n is an integer of 2 ormore); and the first shell space of the first-step reaction zone or thefirst shell space of the second-step reaction zone is controlled in sucha manner that it provides a reactant conversion contribution per lengthas defined in Equation 1 or 2 of 1.2˜2.5.

According to another aspect of the present invention, in the case of asingle-step process for producing unsaturated acids from alkanes, areaction zone for producing the unsaturated acids is divided into two ormore shell spaces by at least one partition; each of the divided shellspaces is independently heat-controlled; a heat transfer medium in thefirst shell space has a temperature ranging from the lowest activetemperature of a catalyst layer packed in a reaction tube correspondingto the first shell space to [the lowest active temperature+20° C.], whenreferring to the two or more shell spaces sequentially as the firstshell space, the second shell space, . . . , the n^(th) shell space; andthe first shell space is controlled in such a manner that it provides analkane conversion contribution per length as defined in Equation 2 of1.2˜2.5.

As used herein, the term “the lowest active temperature of thefirst-step catalyst layer” refers to the lowest temperature where theolefin conversion (defined by the following Equation 3) in the relevantcatalyst layer reaches 90%, when the olefins, such as propylene or thelike, are allowed to react with the relevant catalyst layer at a spacevelocity of about 95˜115 hr⁻¹.

The above space velocity of the olefins ranging from about 95 hr⁻¹ to115 hr⁻¹ corresponds to a space velocity of total reaction feed gasintroduced to the first-step reaction zone of about 1300˜1500 hr⁻¹, thefeed gas comprising 7˜7.5% of olefins, 13˜15% of oxygen, 7˜10% of watersteam and the balance amount of inert gas.

Olefin conversion(%)=[mole number of reacted olefins/mole number ofsupplied olefins]×100  [Equation 3]

As used herein, the term “the lowest active temperature of thesecond-step catalyst layer” refers to the lowest temperature where theunsaturated aldehyde conversion (defined by the following Equation 4) inthe relevant catalyst layer reaches 90%, when the unsaturated aldehydesare allowed to react with the relevant catalyst layer at a spacevelocity of about 75˜100 hr⁻¹.

The above space velocity of the unsaturated aldehydes ranging from about75 hr⁻¹ to 100 hr⁻¹ corresponds to a space velocity of total reactionfeed gas introduced to the second-step reaction zone of about 1050˜1700hr⁻¹, the feed gas comprising 5˜6% of unsaturated aldehydes, 5.5˜6.5% ofoxygen, 1˜2% of unsaturated acid, 12˜17% of water steam, 1˜2% ofbyproducts and the balance amount of inert gas.

Unsaturated aldehyde conversion(%)=[mole number of reacted unsaturatedaldehydes/mole number of supplied unsaturated aldehydes]×100  [Equation4]

Meanwhile, the lowest active temperature of the catalyst layer forproducing unsaturated acids from alkanes refers to the lowesttemperature where the alkane conversion (defined by the followingEquation 5) in the relevant catalyst layer reaches 60%, when the alkanesare allowed to react with the relevant catalyst layer at a spacevelocity of about 50˜80 hr⁻¹.

The above space velocity of the alkanes ranging from about 50 hr⁻¹ to 80hr⁻¹ corresponds to a space velocity of total reaction feed gasintroduced to the reaction zone of about 1500˜2000 hr⁻¹, the feed gascomprising 3˜5% of alkanes, 10˜15% of oxygen, 30˜50% of water steam andthe balance amount of inert gas.

Alkane conversion(%)=[mole number of reacted alkanes/mole number ofsupplied alkanes]×100  [Equation 5]

The lowest active temperature of a catalyst layer depends on the kind ofthe catalyst, content of the catalytic substance in the catalyst layer,ratio of main metal elements in the catalyst, presence of any alkalimetal, kind of the alkali metal, mixing ratio with inactive materials,size of the catalyst, shape of the catalyst, sintering temperature ofthe catalyst, sintering atmosphere of the catalyst, and combinationsthereof.

Generally, the first-step catalyst layer has an active temperature of280˜450° C., while the second-step catalyst layer has an activetemperature of 250˜370° C. Meanwhile, the catalyst layer for producingunsaturated acids from alkanes has an active temperature of 350˜420° C.

The catalyst used in the first-step reaction zone is sintered generallyat a temperature of 400˜600° C., the catalyst used in the second-stepreaction zone is sintered generally at a temperature of 300˜500° C., andthe catalyst used in the reaction zone for producing unsaturated acidsfrom alkanes is sintered generally at a temperature of 500˜600° C. Ifthe highest peak temperature of a catalyst layer exceeds the sinteringtemperature where the catalyst is sintered during the preparationthereof, the catalyst layer is deteriorated, resulting in a drop inyield of the target product.

Additionally, when a catalyst layer is heated due to high reaction heatso that the hot spot temperature of the catalyst layer rapidly increasesor heat accumulation occurs in the vicinity of the hot spot, oxidationforming byproducts such as COx and acetic acid occurs predominantly atsuch high temperature, resulting in a drop in yield of unsaturatedacids.

In general, in the first-step reaction zone and/or the second-stepreaction zone, and the reaction zone for producing unsaturated acidsfrom alkanes via a single-step process, each front portion, for example,the catalyst layer corresponding to the first shell space of each stepshows a high concentration of reactants (olefins, unsaturated aldehydesor alkanes) and a high reaction pressure, and consequently leads to asevere reaction. As a result, a hot spot with a significantly largemagnitude is formed in the front portion of each reaction zone.Therefore, it is preferable that the reaction in the above portion iscontrolled in such a manner that the peak temperature of the relevantcatalyst layer is significantly lower than the sintering temperature ofthe catalyst. Additionally, although each catalyst layer correspondingto the first shell space of each step comprises 20˜30% of the totallength of the catalyst layer, conversion of reactants in the first shellspace reaches 50% or more. In other words, the first shell space has anexcessively high load of reaction in view of its proportion to the totalcatalyst layer, and thus may be thermally unstabilized with ease due tothe high reaction heat.

Therefore, in order to solve the aforementioned problem caused by thefirst shell space of each step, the temperature of the heat transfermedium in the first shell space of each step is decreased possibly tothe lowest active temperature of the catalyst, according to the presentinvention. By doing so, it is possible to control the magnitude of a hotspot and to prevent heat accumulation in the vicinity of the hot spot,while not degrading reactivity severely.

Since a hot spot has a magnitude and a position variable depending onthe kind and activity of the catalyst used in the relevant catalystlayer, the temperature of a heat transfer medium is preferablycontrolled considering the characteristics and reactivity of thecatalyst.

The reactivity of the catalyst layer corresponding to each shell spacecan be expressed by the reactant conversion contribution per length,represented by Equations 1 and 2.

To satisfy the condition of the reactant conversion contribution perlength being 1.2˜2.5, temperature of a heat transfer medium, shearpressure (pressure of the reactor inlet), space velocity, activity of acatalyst, etc. may be controlled.

The partition dividing the first shell space of each step from thesecond shell space of each step is disposed in such a manner that thefirst shell space includes a temperature peak occurring in the inletportion of each reaction zone.

Preferably, the first partition dividing the first shell space from thesecond shell space is disposed in a position corresponding to 25%˜50% ofthe axial length of the reaction zone of each step. This indicates thatcontact time in the first shell space of each step corresponds to about25%˜50% of the total contact time of each step. For example, when thefirst-step reaction zone has a total axial length of 3000 mm, the firstpartition may be disposed at a point of 1200 mm, which corresponds to40% of the total length. However, the first partition should be in sucha position with the proviso that the reactant conversion contribution(defined by Equation 3, 4 or 5) of the first shell space ranges from 1.2to 2.5.

(3) Heat Control of Heat Transfer Medium of Each Shell Space

In the production process and heat exchanger-type reactor according tothe present invention, the temperature of the heat transfer medium ineach shell space is set as nearly as possible to isothermal conditions.According to the amount of heat generation and the capacity of the heattransfer medium, the temperature difference between portions of the heattransfer medium, which correspond to both the ends of a catalyst layerin each of the divided shell spaces, is preferably 0-5° C., and morepreferably 0-3° C.

Examples of the heat transfer medium include a very highly viscousmedium, for example a molten salt which consists mainly of a mixture ofpotassium nitrate and sodium nitrite. Other examples of the heattransfer medium include a phenyl ether medium (e.g., “Dowtherm”),polyphenyl media (e.g., “Therm S”), hot oil, a naphthalene derivative(S.K. oil) and mercury.

By controlling the flow rate of the heat transfer medium, the reactionthroughout the tube corresponding to each of the shell spaces in thereactor can be carried out at substantially the same molten salttemperature.

When heat transfer media filled in shell spaces have differenttemperatures along the flow direction (also referred to as the axialdirection hereinafter) of reactants, reactivity of the relevant catalystlayer varies in proportion to the temperature.

It is preferable to set the temperature of the heat transfer medium(molten salt or heat transfer salt) in each of the divided shell spacesin such a manner that the relevant catalyst layer has optimal activity.

Particularly, the temperature of the heat transfer media can be variedin the axial direction according to the present invention. Thus, it ispossible to inhibit the catalyst from being damaged by an excessivelyhigh exothermic reaction and to prevent degradation in yield of thetarget product, resulting in improvement of the yield.

The temperature of the heat transfer media in the adjacent shell spacesin each of the reaction zones is preferably set to cause a temperaturedifference 0-50° C., and more preferably 5-15° C. along the axialdirection.

In the case of the first-step reaction zone, it is preferred that thetemperature of the heat transfer medium in each of the first shell spaceof the first step, the second shell space of the first step, . . . , then^(th) shell space of the first step, divided by partitions, is set insuch a manner that the temperature of each heat transfer mediumincreases along the axial direction.

In the case of the second-step reaction zone, the heat transfer mediumin each of the first shell space of the second step, the second shellspace of the second step, . . . , the n^(th) shell space of the secondstep, divided by partitions, does not increase or decrease monotonously,because the product of the first step is supplied to the reaction zonecorresponding to the first shell space of the second step. It ispreferred to set the temperature of the heat transfer medium in eachshell space in such a manner that the temperature of the heat transfermedium increases monotonously from the second shell space to the n^(th)shell space except the first shell space, and the temperature of thefirst shell space is set according to the manner as describedhereinafter related to the temperature setting in the second-stepreaction zone.

Meanwhile, in the case of the reaction zone for producing unsaturatedacids from alkanes via a single-step process, it is preferred that thetemperature of the heat transfer medium circulating in each of the firstshell space, the second shell space, . . . , the n^(th) shell space,divided by partitions, is set in such a manner that the temperature ofeach heat transfer medium increases along the axial direction.

Further, according to the present invention it is preferred thatT_(h1)−T^(salt1)≦150° C., more preferably T_(h1)−T_(salt1)≦110° C., andT_(hN)−T_(saltN)≦120° C., more preferably T_(hN)−T_(saltN)≦100° C.(wherein N is an integer of 2 or more), when referring to the shellspaces divided by partitions in the first-step reaction zone forproducing unsaturated aldehydes from olefins or the reaction zone forproducing unsaturated acids from alkanes sequentially as the first shellspace, the second shell space, . . . , the n^(th) shell space.

In addition, it is preferred that T_(h1)−T_(salt1)≦130° C., morepreferably T_(h1)−T_(salt1)≦75° C., and T_(hN)−T_(saltN)≦110° C., morepreferably T_(hN)−T_(saltN)≦70° C. (wherein N is an integer of 2 ormore), when referring to the shell spaces divided by partitions in thesecond-step reaction zone for producing unsaturated acids fromunsaturated aldehydes sequentially as the first shell space, the secondshell space, . . . , the n^(th) shell space.

Herein, T_(h1) is the highest peak temperature of a reaction mixture inthe catalyst layer corresponding to the first shell space (the highestpeak temperature of the catalyst layer), and T_(hN) is the highest peaktemperature of the reaction mixture in the catalyst layer correspondingto the n^(th) shell space (the highest peak temperature of the catalystlayer). Additionally, T_(salt1) is the temperature of the heat transfermedium filled in the first shell space, and T_(saltN) is the temperatureof the heat transfer medium filled in the n^(th) shell space.

In the first shell space, the concentration and pressure of reactantsare high, so that the temperature difference between the highest peaktemperature of the catalyst layer and the temperature of the heattransfer medium is higher than that in the next shell space. For thisreason, the temperature difference range in the first shell space willbe surely wider than those in the next shell spaces. However, thepresent invention provides a method by which the magnitude of peaktemperature in the first shell space is minimized while a temperaturedifference in the next shell space is limited in an extended range,thereby forming an overall temperature profile having a smooth shape.

According to the present invention, the temperature difference betweenthe highest peak temperature of a catalyst layer in each reaction zoneand the temperature of a heat transfer medium is controlled as describedabove, so that the catalyst can show uniform activity in the axialdirection. Thus, it is possible to inhibit heat accumulation in a hotspot and suppress side reactions, thereby preventing a drop in yield.

(4) Constitution of Catalyst Layers

The catalyst layer in the first-step reaction zone may consist of onelayer with axially uniform activity, or if necessary, two or morestacked layers with increasing activity. The catalyst layer in thesecond-step reaction zone may consist of one layer with axially uniformactivity, or if necessary, two or more stacked layers with increasingactivity. The catalyst layer of the reaction zone for producingunsaturated acids from alkanes may be formed in the same manner asdescribed above.

(5) Constitution of Reaction Inhibition Layer

Preferably, a layer formed of an inactive material or a mixture of aninactive material and a catalytic material, i.e., a reaction inhibitionlayer, is disposed within a portion of the catalytic tube, whichcorresponds to a position where the partition is disposed. By doing so,it is possible to eliminate a problem in heat transfer at the positionwhere the partition is disposed.

A commercially available shell-and-tube reactor for producing(meth)acrylic acid includes catalytic tubes in the number of severalhundreds to several tens of thousands, and a partition disposed in sucha reactor has a relatively large thickness of 50˜100 mm. Therefore, inthe reaction zone of each step having two or more divided shell spaces,it is difficult to remove the reaction heat at the portion where apartition is disposed, thereby causing a problem in heat transfer. Tosolve this problem, it is preferred to dispose a layer formed of aninactive material or a mixture of an inactive material and a catalyticmaterial, i.e., a reaction inhibition layer within a portion of thecatalytic tube, which corresponds to a position where the partition isdisposed.

In the reaction inhibition layer, the volume ratio of an inactivematerial to a catalytic material in this reaction inhibition layer is20˜100%.

The inactive material used in the reaction inhibition layer isdesignated as a material which is inactive to a reaction for producingunsaturated aldehydes and/or unsaturated acids from olefins and/oralkanes, for example, catalytic oxidation of propylene or the like and(meth)acrolein. It can be used in a sphere, cylinder, ring, rod, plateor wire mesh shape, or a mass shape with suitable size, or a suitablecombination thereof. Widely known examples of the inactive materialinclude alumina, silica alumina, stainless steel, iron, steatite,porcelain, various ceramics, and mixtures thereof.

Preferably, the reaction inhibition layer is packed to a heightcorresponding to 20˜500% of the thickness of a partition.

The heat control system according to the present invention can beapplied not only to oxidation of olefins but also to a reaction systemfor carrying out different reactions along the axial direction in astepwise manner and a reaction system requiring independent heat controlof every reaction zone to the optimal temperature even if the reactionzones perform the same reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the structure of a reactoraccording to Example 1, which illustrates the position of a partitionand a catalyst layer disposed inside a catalytic tube; and

FIG. 2 is a schematic diagram showing the structure of a reactoraccording to Example 3, which illustrates the position of a partitionand a catalyst layer disposed inside a catalytic tube.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention. It is to be understood that the following examplesare illustrative only and the present invention is not limited thereto.

Reference Example 1 Determination of Lowest Active Temperature ofCatalyst Layer Corresponding to First Shell Space of First Step

A pilot reactor in which the first step is conducted in one catalytictube was provided. The catalytic tube had an inner diameter of 26 mm. Inthe first-step catalytic tube, a catalyst layer was packed to a heightof about 1200 mm. At this time, two kinds of catalysts having activityincreasing along the axial direction from the inlet to the outlet werepacked to a height of 320 mm and 880 mm, respectively (see “Method ofControlling Catalytic Activity” described in U.S. Pat. No. 3,801,634 andU.S. Pat. No. 4,837,360). The catalyst was comprised of the first-stepoxidation catalyst material obtained according to the method asdisclosed in Korean Patent Publication No. 0349602 (Korean PatentApplication No. 10-1997-0045132), the catalyst material being based onmolybdenum (Mo) and bismuth (Bi).

The first catalyst layer (referred to as LGC1 hereinafter) of thefirst-step reaction zone showed an activity corresponding to 85˜90% ofthe catalytic activity of the second catalyst layer, when measuring thecatalytic activity by propylene conversion (space velocity of propylene98 hr−1, molten salt temperature of 300° C.).

Like the following Example 1, the first shell space included the peakportion of the second catalyst layer, and the catalyst layer of thefirst shell space had a length of 540 mm.

The starting materials introduced into the inlet of the reactor werecomprised of propylene, oxygen, steam and nitrogen gas, whereinpropylene content was 7% and the ratio of oxygen to propylene was about1.80. Based on the catalyst layer corresponding to the first shell spaceof the first-step reaction zone (catalyst layer of 540 mm correspondingto the first shell space), space velocity was 1400 hr⁻¹ (standardtemperature and pressure, STP), and space velocity of the olefinsintroduced into the first-step reaction zone was 98 hr⁻¹ (STP)

*Space velocity=flow rate of feed(L/hr,STP)/volume of catalyst layer(L)

The above conditions were the same as those of the following Example 1,with the exception of the space velocity and the temperature of moltensalt.

(1) When the molten salt filled in the first shell space of the firststep was set to a temperature of 285° C., it was shown that propyleneconversion was 86.2% after the analysis of the gas obtained from theoutlet of the first shell space of the first step.

(2) When the molten salt filled in the first shell space of the firststep was set to a temperature of 290° C., it was shown that propyleneconversion was 88.3% after the analysis of the gas obtained from theoutlet of the first shell space of the first step.

(3) When the molten salt filled in the first shell space of the firststep was set to a temperature of 295° C., it was shown that propyleneconversion was 90.8% after the analysis of the gas obtained from theoutlet of the first shell space of the first step.

(4) As can be seen from the above results, the catalyst layer used inReference Example 1 has the lowest active temperature of 290° C.

Example 1 Variations in Yield and in Magnitudes of Temperature Peaks atHot Spots Depending on Variations in Temperature Setting of Molten Salt

As shown in FIG. 1, a pilot reactor was provided in which each offirst-step reaction and second-step reaction is conducted in onecatalytic tube (included in zone 10 or 20 of FIG. 3). The catalytic tubehad an inner diameter of 26 mm, and the first-step catalytic tube wasfilled with catalyst layers to a height of about 1200 mm, and thesecond-step catalytic tube was filled with catalyst layers to a heightof about 1100 mm.

In the catalyst layers of the first step reaction zone 10, two kinds ofcatalysts having activity increasing along the axial direction from theinlet to the outlet were packed to a height of 320 mm and 880 mm,respectively (see “Method of Controlling Catalytic Activity” describedin U.S. Pat. No. 3,801,634 and U.S. Pat. No. 4,837,360). In the catalystlayers of the second-step reaction zone 20, two kinds of catalystshaving activity increasing along the axial direction from the inlet tothe outlet were packed a height of 290 mm and 810 mm, respectively.

The catalyst layers of the first-step reaction zone were comprised ofthe first-step oxidation catalyst material obtained according to themethod as disclosed in Korean Patent Publication No. 0349602 (KoreanPatent Application No. 10-1997-0045132), the catalyst material beingbased on molybdenum (Mo) and bismuth (Bi). The catalyst layers of thesecond-step reaction zone were comprised of a catalyst based onmolybdenum and vanadium (V), the preparation of which is described inKorean patent No. 0204728 or Korean patent No. 0204729.

In the first catalyst layer of the first-step reaction zone, LGC1catalyst was used. The catalyst showed an activity corresponding to85˜90% of the catalytic activity of the second catalyst layer, whenmeasuring the catalytic activity by propylene conversion (space velocityof propylene 98 hr⁻¹, molten salt temperature of 300° C.).

The first catalyst layer of the second-step reaction zone showed anactivity corresponding to 85˜90% of the catalytic activity of the secondcatalyst layer.

A partition was disposed at the 600-mm position (central portion) of thefirst-step reaction zone, so that the first shell space of the firststep covered both temperature peaks occurring in the first catalystlayer of the first step and the second catalyst layer of the first step.In a portion inside the catalytic tube corresponding to the position ofthe partition, an inactive material layer was filled to a thicknesscorresponding 120% of the thickness of the partition.

Reference numerals 11 and 12 in FIG. 1 illustrate the shell spacesdivided in the first-step reaction zone. Each molten salt filled in eachshell space was set to a temperature of 308° C. and 315° C.,respectively. Reference numeral 21 in FIG. 1 illustrate a shell space ofthe second-step reaction zone, the shell space being filled with amolten salt set to a temperature of 265° C.

A pipe inducing a flow represented by reference numeral 2 in FIG. 1serves to connect the two catalytic tubes and is surrounded by a heatinsulation material. Starting materials comprising propylene, steam,oxygen and inert gas enter the reactor through a line 1, passes throughthe reaction steps, and then flows out from the reactor through a line3. The starting materials were comprised of propylene, oxygen, steam andnitrogen gas, wherein the propylene content was 7% and the ratio ofoxygen to propylene was about 1.80. Space velocity was 1400 hr⁻¹(standard temperature and pressure, STP) in the total first-stepreaction zone, and 1530 hr⁻¹ (STP) in the total second-step reactionzone. Also, the space velocity of olefins introduced into the first-stepreaction zone was 98 hr⁻¹ (STP).

In the first shell space of the first step, the value defined byEquation 1 was about 2.

A hot spot was generated in the zone corresponding to the first shellspace of the first-step reaction zone, the hot spot having a temperatureof 392.5° C. After the reaction in the first-step reaction zone,acrolein and acrylic acid were obtained in a yield of 80.33% and 11.37%,respectively. In the second-step reaction zone operated under isothermalconditions, a hot spot having a temperature of 320.5° C. was generated.After the reaction in the second-step reaction zone, acrolein andacrylic acid were obtained in a yield of 0.631% and 86.83%,respectively.

Since no reaction occurred in the reaction inhibition layer (inactivematerial layer), no abnormal increase in temperature caused by a drop inheat transfer efficiency could be observed.

Example 2 Variations in Yield and in Magnitudes of Temperature Peaks atHot Spots Depending on Variations in Temperature Setting of Molten Salt

This example was performed in the same manner as described in Example 1,except that the temperatures of the molten salt in the first-stepreaction zone (first-step reactor) were set to 300° C. and 315° C.,respectively, in an axial direction. In the first shell space of thefirst step, the value defined by Equation 1 was about 1.9.

In the zone corresponding to the first shell space in the first-stepreaction zone, a hot spot with a temperature of 381.2° C. was generated.The yields of acrolein and acrylic acid were 79.02% and 11.46%,respectively. In the second-step reaction zone operated under isothermalconditions, the temperature of a hot spot was 327.5° C., and the yieldsof acrolein and acrylic acid were 0.607% and 84.95%, respectively.

Comparative Example 1

This example was performed in the same manner as described in Example 1,except that the temperature of the molten salt filled in each shellspace of the first-step reaction zone was set to 310° C. Thetemperature, 310° C., of the molten salt in the first-step reaction zoneis higher than the lowest active temperature by 20° C.

In the first-step reactor operated under isothermal conditions, a hotspot with a temperature of 405.7° C. was generated. The yields ofacrolein and acrylic acid were 80.43% and 10.11%, respectively. In thesecond-step reaction zone operated under isothermal conditions, thetemperature of a hot spot was 316.0° C., and the yields of acrolein andacrylic acid were 1.257% and 84.66%, respectively.

After the analysis of the conversion in the portion corresponding to thefirst shell space of the first step according to Comparative Example 1,the value defined by Equation 1 was 2.7.

Comparative Example 2

This example was performed in the same manner as described in Example 1,except that the temperature of the molten salt filled in each shellspace of the first-step reaction zone was set to 320° C. Thetemperature, 320° C., of the molten salt in the first-step reaction zoneis higher than the lowest active temperature by 30° C.

As the highest peak temperature of the first-step catalyst layer exceeds430° C., the catalyst layer was damaged so that the total propyleneconversion decreased rapidly to a level less than 90%. So, the test wasterminated.

Before the catalyst layer was damaged, conversion in the portioncorresponding to the first shell space of the first step according toComparative Example 2 was analyzed. As a result, the value defined byEquation 1 was 3.01.

Comparative Example 3

This example was performed in the same manner as described in Example 1,except that the temperature of the molten salt filled in each shellspace of the first-step reaction zone was set to 312° C. Thetemperature, 312° C., of the molten salt in the first-step reaction zoneis higher than the lowest active temperature by 22° C.

In the first-step reactor operated under isothermal conditions, a hotspot with a temperature of 409.1° C. was generated. The yields ofacrolein and acrylic acid were 78.8% and 11.9%, respectively. In thesecond-step reaction zone operated under isothermal conditions, thetemperature of a hot spot was 329.2° C., and the yields of acrolein andacrylic acid were 0.367% and 85.08%, respectively.

After the analysis of the conversion in the portion corresponding to thefirst shell space of the first step according to Comparative Example 3,the value defined by Equation 1 was 2.63.

TABLE 1 Reaction Comp. Comp. Comp. zone Ex. 1 Ex. 2 Ex. 1 Ex. 2 Ex. 3First Temperature 308 300 310 320 312 step of molten 315 315 310 320 312salt (° C.) Temperature 392.5 381.2 405.7 >430 □ 409.1 of hot spot (°C.) Acrolein 80.33% 79.01% 80.43% —  78.8% Acrylic acid 11.37% 11.46%10.11%  11.9% Second Temperature 265 265 265 265 265 step of molten salt(° C.) Temperature 320.5 327.5 316.0 — 329.2 of hot spot (° C.) Acrolein0.631% 0.607% 1.257% — 0.367% Acrylic acid 86.83% 84.95% 84.66% — 85.08%

Reference Example 2 Determination of Lowest Active Temperature ofCatalyst Layer Corresponding to First Shell Space of Second Step

A pilot reactor in which the first-step reaction and the second-stepreaction are conducted in one catalytic tube was provided. The catalytictube had an inner diameter of 26 mm. In the catalytic tube, a first-stepcatalyst layer was packed to a height of about 3570 mm, and thesecond-step catalyst layer was packed to a height of about 3125 mm.Herein, the catalyst material filled in the first-step reaction zone(reference numeral 10 in FIG. 2) was the first-step oxidation catalystmaterial obtained according to the method as disclosed in Korean PatentPublication No. 0349602 (Korean Patent Application No. 10-1997-0045132),the catalyst material being based on molybdenum (Mo) and bismuth (Bi).The three catalyst layers filled in the second-step reaction zone(reference numeral 20 in FIG. 2) were comprised of a catalyst based onmolybdenum and vanadium (V), the preparation of which is described inKorean patent No. 0204728 or Korean patent No. 0204729.

The second-step catalyst layers were comprised of three kinds ofcatalysts having activity increasing along the axial direction from theinlet to the outlet (see “Method of Controlling Catalytic Activity”described in U.S. Pat. No. 3,801,634 and U.S. Pat. No. 4,837,360). Thefirst catalyst layer (reference numeral 21 in FIG. 2) of the second-stepreaction zone, from which the second-step reaction started, showed anactivity corresponding to about 20% of the catalytic activity of thethird catalyst layer of the second step (reference numeral 23 in FIG.2). This was accomplished by forming the first catalyst layer with amixture containing 20 wt % of the same catalyst material as the thirdcatalyst layer and 80 wt % of an inactive material. The second catalystlayer of the second step (reference numeral 22 in FIG. 2) showed anactivity corresponding to 87% of the catalytic activity of the thirdcatalyst layer of the second step.

The three catalyst layers of the second-step reaction zone were packedto a height of 500 mm, 700 mm and 1925 mm, respectively, along the axialdirection. The first catalyst layer of the second step was packed to aheight of 250 mm in the catalytic tube corresponding to the shell spacesof the second-step reaction zone, and the remaining 250 mm was disposedin the partition (reference numeral 30 in FIG. 2), by which thefirst-step reaction zone was divided from the second-step reaction zone,and in the catalytic tube covering the shell spaces of the first-stepreaction zone.

The second-step reaction zone was divided into two independent shellspaces (reference numerals 24 and 25 in FIG. 2) by the partition(reference numeral 27 in FIG. 2) disposed in the boundary between thesecond catalyst layer of the second step and the third catalyst layer ofthe second step. Meanwhile, an inactive material layer was packed in thecatalytic tube at the portion corresponding to the position of thepartition to a height corresponding to 120% of the thickness of thepartition.

The starting materials introduced into the inlet of the second-stepreaction zone (i.e., the partition 30 by which the first-step reactionzone was divided from the second-step reaction zone) were comprised ofacrolein, acrylic acid, oxygen, steam and nitrogen gas, moreparticularly, 5.5% of acrolein, 0.9% of acrylic acid, 5.0% of oxygen,1.0% of byproducts such as COx and acetic acid, and the balance amountof nitrogen gas.

In the catalyst layers corresponding to the first shell space of thesecond-step reaction zone (catalyst layer of 950 mm corresponding to 250mm of the first catalyst layer combined with 700 mm of the secondcatalyst layer), space velocity was 1500 hr⁻¹ (standard temperature andpressure, STP). Herein, space velocity of the hydrocarbon reactant, i.e.acrolein, introduced into the second-step reaction zone was 81 hr⁻¹(STP) and the feed gas mixture had a pressure of 0.4 kgf/cm²G.

The above conditions were the same as those of the following Example 3,with the exception of the space velocity and the temperature of moltensalt.

(1) When the molten salt filled in the first shell space of the secondstep was set to a temperature of 255° C., it was shown that theconversion defined by Equation 4 was 83.1% after the analysis of the gasobtained from the outlet of the first shell space of the second step.

(2) When the molten salt filled in the first shell space of the secondstep was set to a temperature of 260° C., it was shown that theconversion defined by Equation 4 was 91.9% after the analysis of the gasobtained from the outlet of the first shell space of the second step.

As can be seen from the above results, the catalyst layer has the lowestactive temperature of 260° C.

Example 3 Use of Mixed Layers and Multi-step Heat Control System

A pilot reactor in which the first-step reaction and the second-stepreaction are conducted in one catalytic tube was provided. The catalytictube had an inner diameter of 26 mm. In the catalytic tube, a first-stepcatalyst layer was packed to a height of about 3570 mm, and thesecond-step catalyst layer was packed to a height of about 3125 mm.Herein, the catalyst material filled in the first-step reaction zone(reference numeral 10 in FIG. 2) was the first-step oxidation catalystmaterial obtained according to the method as disclosed in Korean PatentPublication No. 0349602 (Korean Patent Application No. 10-1997-0045132),the catalyst material being based on molybdenum (Mo) and bismuth (Bi).The three catalyst layers filled in the second-step reaction zone(reference numeral 20 in FIG. 2) were comprised of a catalyst based onmolybdenum and vanadium (V), the preparation of which is described inKorean patent No. 0204728 or Korean patent No. 0204729.

The second-step catalyst layers were comprised of three kinds ofcatalysts having activity increasing along the axial direction from theinlet to the outlet (see “Method of Controlling Catalytic Activity”described in U.S. Pat. No. 3,801,634 and U.S. Pat. No. 4,837,360). Thefirst catalyst layer (reference numeral 21 in FIG. 2) of the second-stepreaction zone, from which the second-step reaction started, showed anactivity corresponding to about 20% of the catalytic activity of thethird catalyst layer of the second step (reference numeral 23 in FIG.2). This was accomplished by forming the first catalyst layer with amixture containing 20 wt % of the same catalyst material as the thirdcatalyst layer and 80 wt % of an inactive material. The second catalystlayer of the second step (reference numeral 22 in FIG. 2) showed anactivity corresponding to 87% of the catalytic activity of the thirdcatalyst layer of the second step.

The three catalyst layers of the second-step reaction zone were packedto a height of 500 mm, 700 mm and 1925 mm, respectively, along the axialdirection. The first catalyst layer of the second step was packed to aheight of 250 mm in the catalytic tube corresponding to the shell spacesof the second-step reaction zone, and the remaining 250 mm was disposedin the partition (reference numeral 30 in FIG. 2), by which thefirst-step reaction zone was divided from the second-step reaction zone,and in the catalytic tube covering the shell spaces of the first-stepreaction zone.

The second-step reaction zone was divided into two independent shellspaces (reference numerals 24 and 25 in FIG. 2) by the partition(reference numeral 27 in FIG. 2) disposed in the boundary between thesecond catalyst layer of the second step and the third catalyst layer ofthe second step.

Each molten salt filled in each shell space was set to a temperature of275° C. and 270° C., respectively. Meanwhile, an inactive material layerwas packed in the catalytic tube at the portion corresponding to theposition of the partition to a height corresponding to 120% of thethickness of the partition (reference numeral 26 in FIG. 2).

The starting materials introduced into the inlet of the second-stepreaction zone, (i.e. the partition 30, by which the first-step reactionzone was divided from the second-step reaction zone) were comprised ofacrolein, acrylic acid, oxygen, steam and nitrogen gas, moreparticularly, 5.5% of acrolein, 0.9% of acrylic acid, 5.0% of oxygen,1.0% of byproducts such as COx and acetic acid, and the balance amountof nitrogen gas. In the total second-step reaction zone, space velocitywas 1500 hr⁻¹ (standard temperature and pressure, STP). Herein, spacevelocity of the hydrocarbon reactant, i.e. acrolein, introduced into thesecond-step reaction zone was 81 hr⁻¹ (STP) and the feed gas mixture hada pressure of 0.4 kgf/cm²G.

In the reaction zone corresponding to the first shell space of thesecond step, the value defined by Equation 2 was about 2.

In the second-step reaction zone, two catalyst layers of the threecatalyst layers except the mixed layer (i.e. the first catalyst layer)had a temperature peak. The two peak temperatures were 309.4° C. and321.7° C. along the axial direction. When the propylene contentintroduced into the first step was 7.0%, yield of acrylic acid was86.2%. Yields of byproducts, COx (carbon monoxide and carbon dioxide)and acetic acids, were 8.51% and 1.80%, respectively.

The reaction mixture arriving in the first catalyst layer of the secondstep along the axial direction had a temperature of 316° C., and thetemperature difference between the above temperature and the first heattransfer medium of the second step was 41° C.

Comparative Example 4

This example was performed in the same manner as described in Example 3,except that the temperature of the molten salt filled in each shellspace of the second-step reaction zone was set to 285° C. Thetemperature, 285° C., is higher than the lowest active temperature by25° C., and thus is not included in the scope of the present invention.

In the reaction zone corresponding to the first shell space of thesecond step according to Comparative Example 4, the value defined byEquation 2 was about 2.2, which was included in the scope of the presentinvention. In the second-step reaction zone, two catalyst layers of thethree catalyst layers except the mixed layer (i.e. the first catalystlayer) had a temperature peak. The two peak temperatures were 331.3° C.and 328.1° C. along the axial direction. Yield of acrylic acid was83.8%, and the yields of byproducts, COx (carbon monoxide and carbondioxide) and acetic acid were 11.3% and 2.12%, respectively.

TABLE 2 Reaction zone Ex. 3 Comp. Ex. 4 Second Temperature of 275 285step molten salt (° C.) 270 285 Temperature of 309.4 331.3 hot spot (°C.) 321.7 328.1 Acrylic acid 86.2% 83.8%

INDUSTRIAL APPLICABILITY

As described above, the present invention provides an improved system inwhich the temperature of a heat transfer medium in each shell space iscontrolled depending on the activity of a catalyst and the degree ofreaction. By doing so, it is possible to inhibit heat accumulation in ahot spot and the vicinity thereof, and thus to ensure thermal stability,to reduce the production of byproducts and to improve the yield of afinal product.

1. A shell-and-tube heat exchanger-type reactor which can be used in aprocess for producing unsaturated aldehydes and unsaturated acids fromolefins by fixed-bed catalytic partial oxidation, the reactor comprisingone or more catalytic tubes each including a first-step reaction zonefor mainly producing the unsaturated aldehydes, and a second-stepreaction zone for mainly producing the unsaturated acids, or both thetwo zones, wherein at least one of the first-step reaction zone and thesecond-step reaction zone is divided into two or more shell spaces by atleast one partition; each of the divided shell spaces is independentlyheat-controlled; a heat transfer medium in the first shell space of thefirst-step reaction zone or the first shell space of the second-stepreaction zone has a temperature ranging from the lowest activetemperature of a catalyst layer packed in a reaction tube correspondingto the first shell space of the first-step reaction zone or the firstshell space of the second-step reaction zone to the lowest activetemperature of the catalyst layer plus 20° C., wherein the two or moreshell spaces corresponding to the first-step reaction zone aresequentially referred to as the first shell space of the first-stepreaction zone, the second shell space of the first-step reaction zone, .. . , the n^(th) shell space of the first-step reaction zone, and thetwo or more shell spaces corresponding to the second-step reaction zoneare sequentially referred to as the first shell space of the second-stepreaction zone, the second shell space of the second-step reaction zone,. . . , the n^(th) shell space of the second-step reaction zone; and thefirst shell space of the first-step reaction zone or the first shellspace of the second-step reaction zone is controlled in such a mannerthat it provides a reactant conversion contribution per length asdefined in a following equation of 1.2˜2.5:Olefin conversion contribution per length=(mole number of olefins thathave reacted in the relevant catalyst layer zone/mole number of thetotal olefins supplied to the first-step reaction zone)/volumetric ratioof the relevant catalyst layer zone to the total first-step catalystlayer of the first-step reaction zone, orUnsaturated aldehyde conversion contribution per length=(mole number ofunsaturated aldehydes that have reacted in the relevant catalyst layerzone/mole number of the total unsaturated aldehydes supplied to thesecond-step reaction zone)/volumetric ratio of the relevant catalystlayer zone to the total catalyst layer of the second-step reaction zone.2. A shell-and-tube heat exchanger-type reactor which can be used in aprocess for producing unsaturated acids from alkanes by fixed-bedcatalytic partial oxidation, the reactor comprising one or morecatalytic tubes each including a reaction zone for producing theunsaturated acids, wherein the reaction zone is divided into two or moreshell spaces by at least one partition; each of the divided shell spacesis independently heat-controlled; a heat transfer medium in the firstshell space has a temperature ranging from the lowest active temperatureof a catalyst layer packed in a reaction tube corresponding to the firstshell space to the lowest active temperature of the catalyst layer plus20° C.], wherein the two or more shell spaces are sequentially referredto as the first shell space, the second shell space, . . . , the n^(th)shell space; and the first shell space is controlled in such a mannerthat it provides an alkane conversion contribution per length as definedin a following equation of 1.2˜2.5:alkane conversion contribution per length=(mole number of alkanes thathave reacted in the relevant catalyst layer zone/mole number of thetotal alkanes supplied to the reaction zone)/volumetric ratio of therelevant catalyst layer zone to the total catalyst layer of the reactionzone.
 3. The shell-and-tube heat exchanger-type reactor according toclaim 1, wherein the first-step reaction zone is for producing(meth)acrolein from at least one compound selected from the groupconsisting of propylene, isobutylene, t-butyl alcohol, methyl-t-butylether and o-xylene.
 4. The shell-and-tube heat exchanger-type reactoraccording to claim 1, wherein the second-step reaction zone is forproducing (meth)acrylic acid from (meth)acrolein.
 5. The shell-and-tubeheat exchanger-type reactor according to claim 2, which is for producing(meth)acrylic acid from propane or isobutane.
 6. The shell-and-tube heatexchanger-type reactor according to claim 1, wherein the partitiondividing the first shell space from the second shell space is disposedin such a manner that the first shell space covers a temperature peakgenerated in a front portion of each reaction zone.
 7. Theshell-and-tube heat exchanger-type reactor according to claim 6, whereinthe partition dividing the first shell space from the second shell spaceis disposed in a position corresponding to 25%˜50% of the axial lengthof each reaction zone.
 8. The shell-and-tube heat exchanger-type reactoraccording to claim 2, wherein the partition dividing the first shellspace from the second shell space is disposed in such a manner that thefirst shell space covers a temperature peak generated in a front portionof each reaction zone.
 9. The shell-and-tube heat exchanger-type reactoraccording to claim 8, wherein the partition dividing the first shellspace from the second shell space is disposed in a positioncorresponding to 25%˜50% of the axial length of each reaction zone. 10.The shell-and-tube heat exchanger-type reactor according to claim 1,wherein the first shell space of the first-step reaction zone, thesecond shell space of the first-step reaction zone, . . . the n^(th)shell space of the first-step reaction zone, divided by the partitionsare controlled in such a manner that temperature of the heat transfermedium circulating in each shell space increases along the axialdirection.
 11. The shell-and-tube heat exchanger-type reactor accordingto claim 1, wherein the second shell space of the second-step reactionzone through the n^(th) shell space of the second-step reaction zonedivided by the partitions are controlled in such a manner thattemperature of the heat transfer medium circulating in each shell spaceincreases along the axial direction.
 12. The shell-and-tube heatexchanger-type reactor according to claim 2, wherein the first shellspace, the second shell space, . . . , the n^(th) shell space divided bythe partitions are controlled in such a manner that temperature of theheat transfer medium circulating in each shell space increases along theaxial direction.
 13. The shell-and-tube heat exchanger-type reactoraccording to claim 1, wherein T_(h1)−T_(salt1)≦150° C., andT_(hN)−T_(saltN)≦120° C. in the first-step reaction zone for producingunsaturated aldehydes from olefins (wherein N is an integer of 2 ormore; T_(h1) is the highest peak temperature of a reaction mixture in acatalyst layer corresponding to the first shell space; T_(hN) is thehighest peak temperature of a reaction mixture in a catalyst layercorresponding to the n^(th) shell space; T_(salt1) is the temperature ofa heat transfer medium filled in the first shell space; and T_(saltN) isthe temperature of a heat transfer medium filled in the n^(th) shellspace.
 14. The shell-and-tube heat exchanger-type reactor according toclaim 1, wherein T_(h1)−T_(salt1)≦130° C., and T_(hN)−T_(saltN)≦110° C.in the second-step reaction zone for producing unsaturated acids fromunsaturated aldehydes (wherein N is an integer of 2 or more; T_(h1) isthe highest peak temperature of a reaction mixture in a catalyst layercorresponding to the first shell space; T_(hN) is the highest peaktemperature of a reaction mixture in a catalyst layer corresponding tothe n^(th) shell space; T_(salt1) is the temperature of a heat transfermedium filled in the first shell space; and T_(saltN) is the temperatureof a heat transfer medium filled in the n^(th) shell space.
 15. Theshell-and-tube heat exchanger-type reactor according to claim 2, whereinT_(h1)−T_(salt1)≦150° C., and T_(hN)−T_(saltN)≦120° C. (wherein N is aninteger of 2 or more; T_(h1) is the highest peak temperature of areaction mixture in a catalyst layer corresponding to the first shellspace; T_(hN) is the highest peak temperature of a reaction mixture in acatalyst layer corresponding to the n^(th) shell space; T_(salt1) is thetemperature of a heat transfer medium filled in the first shell space;and T_(saltN) is the temperature of a heat transfer medium filled in then^(th) shell space.
 16. The shell-and-tube heat exchanger-type reactoraccording to claim 1, wherein a reaction inhibition layer formed of aninactive material alone or a mixture of inactive materials and acatalyst is placed within the catalytic tube in a position correspondingto the position of the partition.
 17. The shell-and-tube heatexchanger-type reactor according to claim 2, wherein a reactioninhibition layer formed of an inactive material alone or a mixture ofinactive materials and a catalyst is placed within the catalytic tube ina position corresponding to the position of the partition.